Study On The Influence Of Typical Modified Substrate And Plant On The Runoff Quality Of Green Roof

As an important green infrastructure at the source of sponge city,green roof can regulate the runoff and water quality of the roof.With the continuous development of the concept of stormwater management,green roof has gradually become a much concerned facility due to its environmental benefits.However,with the diversified development of structural parameters and the changes of structural functions during operation,the effect and mechanism of green roofs on runoff water quality are still unclear.On this basis,the substrate and vegetation of green roof were taken as the breakthrough point in this study.By monitoring the changes of main components of typical modified substrates,the growth status of commonly used plants,and the characteristics of runoff water quality during rainfall,the response relationship among substrates,plants and runoff was systematically analyzed.The conclusions of this paper were as follows:（1）Biochar and organobentonite enhanced the physical structure and water-holding capacity of the substrate,and enhanced the nutrient retention ability and enzyme activity regulation ability of the substrate during rainfall,which made the green roof substrate have a higher nutritional level,and the effect of organobentonite was better.Organic matter and available phosphorus of green roof substrate did not decrease continuously with rainfall,while available nitrogen decreased continuously with rainfall.After simulated rainfall,the soil phosphatase activity of the substrate was decreased,the catalase activity was increased,and the urease activity was significantly increased.（2）Through monitor that plant growth physiology and the nutrition state,the stronger the ability of plants to absorb nutrients from the substrate,the better nutritional status of plant and the better plant growth status.Two typical modified substrates could improve the physiological performance and nutritional status of plants.Among them,could increase biomass,TOC and N content of aboveground parts of plants,biochar could increase plant height and chlorophyll content,and organobentonite could increase P content of plants.（3）Green roof could significantly reduce runoff,improve runoff retention rate and delay runoff production time,but its control effect on rainstorm was not significant.Runoff retention effect decreased with the increase of return period and increased with the increase of antecedent dry weather period,and the return period has stronger influence on runoff retention effect than antecedent dry weather period.The cumulative runoff retention effect of green roof decreased linearly with the increase of cumulative rainfall.The runoff retention effect of biochar green roof was greatly affected by return period,while the runoff retention effect of organobentonite green roof was greatly affected by antecedent dry weather period.（4）The three green roofs had better reducing effect on runoff SS,but they were the release sources of runoff COD,TN,NO₃^--N,NH₄⁺-N,TP and PO ₄^3--P.Phosphorus leaching was mainly PO ₄^3--P,and nitrogen leaching was mainly NO₃^--N.The runoff COD,TN,NO₃^--N and NH₄⁺-N concentrations of three green roofs decreased exponentially with the cumulative rainfall,while the runoff TP and PO ₄^3--P concentrations of traditional green roof and organobentonite green roof decreased linearly with the cumulative rainfall.Biochar and organobentonite could reduce the leaching of COD,TN and NO₃^--N,but biochar could aggravate the leaching of NH₄⁺-N,TP and PO ₄^3--P.（5）The runoff nitrogen leaching and organic matter leaching of green roofs ware closely influenced by substrates and plants,while the phosphorus leaching process was relatively stable.Organic matter and nitrogen leaching were directly affected by changes in total nitrogen content of substrate,and indirectly affected by changes in p H and available nitrogen content of substrate.Substrate available nitrogen affected runoff quality by changing other chemical properties of substrate and affecting plant growth,which was the most critical factor affecting runoff organic matter and nitrogen leaching in green roof.The growth state of plants could affect the organic matter leaching of runoff,but had a weak effect on nitrogen leaching.